Electrostatic printing method and apparatus



July 3, 1951 w. J. HooPl-:R 2,558,900

ELECTROSTATIC PRINTING METHODS AND APPARATUS July 3, 1951 w. J. HooPER 2,558,900

ELECTROSTATIC PRINTING METHODS AND APPARATUS Filed March 26, 1945 3 Sheets-Sheet 3 Patented July 3, 1951 ELECTROSTATIC PRINTING METHOD AND APPARATUS William J. Hooper, Elsah, Ill., assgnor, by mesne assignments, to William C. Huebner, New York,

Application March 26, 1945', Serial No. 584,835

2 Claims.

This invention relates to printing methods and apparatus, and more particularly to apparatus wherein there is insufficient contact pressure between th`e printing means and the sheet being printed to effect proper transfer of the ink, and wherein good transfer is achieved by virtue of the presence of an electric field of force.

One feature of this invention is that it achieves all of the advantages of electric printing (such as lightweight parts, high speed of operation, etc.) while at the same time securing better definition and printing with the use of lower field strengths by letting at least portions of the sheet being printed come into, light contact with the ink on at least portions of the design bearing surface, this contact being so light as to be insufcient for proper printing in the absence of the electric field and therefore not requiring heavy pressure or strong and heavy parts.

Another feature of this invention is that it provides improved means for transferring a liquid,

A as ink, to a sheet, as a moving web of paper; still another feature of this invention is that conditions are created such that a high degree of eflciency of transfer by the electric field is achieved; and a further feature of this invention is that it provides improved means for preconditioning the web or sheet before moving it into the printing zone. Other features and advantages of this invention will be apparent from the following specification and the drawings, in which:

Figure 1 is an elevational view, partly schematic, of one specific embodiment of my inventions, an electric printing press of the kind wherein the lweb being printed is passed sufficiently closely adjacent a rotated inked type cylinder to make very light contactwith the ink on the surface of at least portions of the type cylinder; Figure 2 is an enlarged fragmentary detail view of the printing zone of the apparatus of Figure 1; Figure 3 is a view similar to Figure 1, but of another embodiment of my inventions; and Figure 4 is still another elevational view, partly schematic, of still another specific embodiment oi' my inventions.

Printing has for centuries been conventionally effected by mechanical pressure between an inked member having a design thereon and the sheet to be printed. Very recently, however, it has been found that ink can be transferred from the inked member to the sheet being printed by the use of a field of force, either magnetic or electrostatic, without actual contact between the inked member and the sheet. Certain arrangements heretofore proposed for electric printing are shown in such 2 patents as Huebner Patent 1,820,194 of August 25, 1931, and Huebner Patent 2,224,391 of December 10, 1940, although these arrangements have never gone into commercial use. A full discussion of this type of printing will not be set forth here, as reference may be made to the above-mentioned patents to supplement the present disclosure in regard to the advantages being sought. It is believed suflicient to say that elimination of all need for mechanical pressure enables Very great reductions in the weight and power requirements of a large press, a goal toward which the printing industry has been working for decades.

All electric printing heretofore done has involved the transfer of the ink across a definite and appreciable space; i. e., the film of ink on the raised portions of a type cylinder, for example, had to be physically separated from such cylinder and caused to move across a space of several hundredths of an inch to the surface of the web or sheet on which printing was to be done. Surface tension, adherence of the ink to the metal of the type cylinder, and the like, are strong factors resisting the movement of small droplets or particles of ink away from the film of inkon the ink source, and high field strengths and means for facilitating initiation of such movement have heretofore had to be employed. I have found that all of the benefits of this type of electric printing can be retained, with better and easier transfer of the ink, by bringing the moving web into very light conta'ct with the surface of the film of ink on the design bearing cylinder. This contact is not sufficiently heavy to effect satisfactory printing in the conventional manner, as this would require pressures and strengths which would lose the advantages of electric printing; but, by cutting down the space of movement of the ink to the absolute minimum, and even by having at least portions of the ink on the design bearing surface in actual contact with the web at the point of printing, factors such as adherence to and absorption in the web tend to assist the field in separating the desired amount of ink from the design bearing cylinder. The conventional type cylinder may have certain areas or portions of its raised type surface two or three thousandths of an inch higher than other parts, but in general the cylinder presents what may be considered a plane surface at the printing point. The film of ink on the type faces is quite thin, but the arrangement should be such that the web may touch the upper surface of the ink film lightly on the lower type faces without coming into unduly heavy Apressure relations with the higher type faces. Even if some particular section of the cylinder should be exceptionally low, so that no contact with the ink film occurs there, the system I am here disclosing would result in reduction of the transfer space to only a very few thousandths of an inch, as contrasted with a space of fifteen or twenty thousandths of an inch.

In view of the newness of electric printing, terminology peculiar to this art has not as yet come into common use, and the words used throughout this specification and claims will be those employed in the conventional printing art wherein ink transfer is effected by mechanical pressure. That is, for example, the term printing is used to describe the operation of delivering ink from the inked member to the sheet being printed, although it will be understood that the word printing as used herein does not connote any mechanical pressure, but is used in the vmuch broader sense of the word merely to mean transfer of a certain design from one element to another. This is analogous to the use of the term printing in photography, where mechanical pressure is not the cause of transference of a design from thenegative to the sensitized paper. It will be also understood that when one of the rolls or printing members is spoken of as having designs formed on the surface thereof, such designs may comprise text, pictures, or anything else desired to be printed. Moreover. the designs may be formed onI the surface of the printing member in relief, by intaglio or gravure, or by planographic or lithographie methods. All such methods of forming or preparing a printing surface are well known in the conventional printing art and need not be described here, as is also the case in connection with methods and apparatus for delivering ink to the inked surface in desired quantities. in reading and interpreting this specification and the claims accompanying it, all terminology borrowed from the conventional printing art must be given broad meaning appropriate to this rather special eld.

. Reference Iis made herein to another of my inventions in the field of electric printing as disclosed in my copending application Serial No. 564,574, filed November 22, 1944, and issued August 29, 1950, as Patent 2,520,504.

Referring now more particularly to the specific printing apparatus shown in Figures l and 2 of the accompanying drawings, a rotating type cylinder i acts as an ink source and as one of the electrode members for creating an. electric field across the printing space. This cylinder is mounted in conventional manner, not illustrated, to be rotatable about its axis il, and it is electrically grounded throughout. The designs, here illustrated as in relief on the surface of the cylinder, are inked by means here illustrated schematically as conventional inking means comprising the ink trough i2 and the rolls ISaf-d. Rotation of the cylinder I0 results in continually presenting to the printing point or space (directly above the axis of the cylinder, as illustrated here) a surface area which is at least partly coated with ink in the desired design to be transferred. the raised portions of the type in the case here illustrated carrying ink and the other portions of the surface being devoid of inlft.

The sheet to be printed is here illustrated as a web of paper i4, as a web of the kind used in newspaper printing. This web moves over a preconditioning and bearing member i5, in contact with a portion of the periphery of another rotating cylinder I6, and then over the guide roller I8. This web I4 is, of course, driven by conventional web drive means so as to have a lineal speed synchronized with the surface speed of the type cylinder I0.

The guide and preconditioning member I5 lis preferably of some solid non-corrosive material which. in the Tribo-electricy series, is negative with respect to paper, as silver. -This member I5 is grounded, and the eiect of movement of the web I4 thereover is to create a positive electrostatic charge on such web as it moves away from the element I5. This charge serves to condition the paper, as has been more fully described and claimed in one of my above-mentioned earlier led applications, so as to render the electric field at the printing point most effective. A pair of Wedge-shaped members I9 and 20 of plate glass. preferably having a relatively low dielectric constant, serve as printing gap defining members, as has been mode fully described and claimed in certain of my above-mentioned earlier filed applications. The adjacent edges of the members i 9 and 20, as may be best seen in Figure 2, define a gap which may be in the neighborhood of a half inch to an inch wide and which runs the full length of the cylinder I0, printing or transfer taking place entirely on the portion of the web within this gap.

The electric field -at the printing point is developed between the cylindrical member I0, as one electrode, and the surface of the cylindrical member I6, as the other electrode. The cylindrical member EIS comprises an inner portion IEa of metal, and an outer portion b of material having what might be termed only moderately high resistance to current flow, as for example a layer of conducting rubber between a quarter and a half inch thick. Rubber so impregnated as to let appreciable current flow therethrough is commercially available under the designation of conducting rubber, and the particular rubber which l am here disclosing might have a resistance in the neighborhood of 25,000 ohms per cubic centimeter, and should preferably be quite resilient. When current is delivered to the inner metal portion of the cylindrical member i6 at a certain voltage, the resistance per cubic centimeter through this outer rubber layer being known, a desired predetermined quantity of current can be caused to ilow to a'given surface area of the roll, through the roll, between one printing operation and the next of such given increment or unit of area. At the same time, the electrical resistance is high enough to prevent any appreciable transfer of electricity between adjacent increments of area at the instant of printing, and to prevent the formation of arcs, the'current capable of traveling through the rubber surface at the instant of printing being insufficient to support an arc.

The potential differential between the cylindrical members or electrodes is developed by a variable high potential source here identified as 2|. This source is adapted to develop a relatively high direct current potential between ground and its high voltage or hot output terminal, this terminal being connected to the elec-A trode cylinder I6 through a variable current controlling resistance here identified as 22. This high voltage source may be of a conventional type which can be secured on the commercial market, as for example those built for high voltage X-ray tube supply purposes. Such equipment takes power from an ordinary commercial alternating current source, steps its voltage' up age and current may be determined, and the like.

The equipment is not being further described or illustrated in detail, as it is well known and commercially available in forms to meet the voltage and current requirements of apparatus of this type. While the current requirements for electric printing are not heavy in the ordinary sense of the word, a very definite electron current or space current ow across the printing space at the instant of printing is desirable and, to get a space current of one or two milliamperes per square inch of printing area at the instant of printing, the high potential source should be capable of maintaining the desired voltage under current drains in the neighborhood of 100 milliamperes, or even slightly more.

As has been more fully described and claimed in my earlier applications, I prefer to have the electrode member behind the ink, the member away from which the ink travels during printing or transfer, negative with respect to the other electrode member; i. e., in the press here illustrated, the cylindrical electrode. member I6 would be charged positively with respect to ground, so that the cylindrical member I0 is the negative electrode in so far as the electric eld is concerned. It may be that the minute ink droplets (conventional ink having graphite pigment particles suspended in an oil base has negatively charged particles) have their movement away from the inked surface assisted by having electrons leave such surface from behind the ink in the direction in which it is desired to move the ink, or it may be that an ion bombardment eifect analogous to that taking place in cathode sputtering of metals assists in breaking the ink droplets loose from the remainder of the ink lm and initiating their movement. Whatever the reason, however, the ink does move more readily from the inked surface to the web when such surface is negative with respect to the web and the electrode to the other side of the web. Accordingly I illustrate the high potential source as having its negative terminal grounded and its positive terminal connectedthrough the variable resistance 22 to the cylindrical electrode member I6.

Referring now more particularly to Figure 2, it will be seen that the spacing between the cylindrical members I0 and I6 is such that the lower surface of the web i4 just touches the upper surface of the lm of ink 23 on the raised type faces of the cylinder I0. This contact is preferably just a kiss contact, with insuflicient mechanical pressure to force the ink into the fibers of the paper and eiect printing in conventional manner. The desirable condition is to just have the lower surface of the web I4 just touch the upper surface of the lm of ink 23, so that at the instant of printing (as shown by the center raised portion of the type roll in Figure 2) the ink m on this particular portion has one side thereof in physical contact with the type face and the other side thereof in physical contact with the lower surface of the cooperating portion of the web i4. The movement of ink into the fibers of the paper sufficiently to result in the desired impressionfor printing is then effected by the forces developed by the electric field existing between the adjacent chargedA surface ofthe other cylinder I6, this being aided by thepositive charge present on the. paper due to the conditioning by the silver rubbing block I5. Heavy pressure of the kind found in conventional printing must be avoided; but printing is not defeated if some small portion of the type cylinder is sulciently lower than the others that there is a thousandth of an inch or two space between the parts. as the spacing has in any event been reduced considerably below anything heretofore thought posmeter and preferably considerably higher.

sible or desirable in electric printing. l

Figure 3 shows another embodiment of my invention making use of what may be termed the light contact or kiss contact, aided by electric ileld forces. In order to simplify and shorten the description of the apparatus shown in Figure 3, parts thereof which are analogous to those heretofore described in connection with the apparatus shown in Figures l and 2 will be given reference numerals 20 higher than those'used in the description of the lrst two gures.

In this form of my invention shown in Figure 3, the design bearing roll is again shown as a type roll, being here identified as 30, all parts of this cylindrical member being grounded. Inking is effected by inking means comprising the trough 32 and the inking rolls 33e-d. A web of paper 34 is shown as passing over guide means 35i, here shown simply as a guide roll, in contact with a portion of the periphery of a roll 36, and over another guide roll 38. The printing space is again defined by wedge-shaped glass members here identified as 39 and 46. The potential differential necessary to create the desired electric field between the cylindrical members 30 and 36 again compriss a variable high potential source of a type available on the commercial market, here identified as 4I, having itsI negative terminal grounded and its positive or hot" terminal connected to variable resistance 42 which is in turn connected to a metal roll or cylindrical member 44.

In this particular form of my invention the roll 36 has an inner cylindrical metal portion 36a which is grounded, and an outer layer 36h of rubber having a relatively high dielectric constant and of very high specific resistivity, at least ten to the tenth power ohms per cubic centi- The rubber layer in this case, which may be about one-quarter of an inch thickness and should be quite resilient, acts as the dielectric medium between condenser plates comprising the inner metal portion 36a and the surface of the roll 4t, at least in the portions where these parts are adjacent each other. Inasmuch as the part 36a is grounded and the part 44 is at a considerable positive potential with respect to ground, a charge is deposited on the outer surface of the rubber layer 36h and carried around to the printing point. By proper proportioning of the capacities involved (taking into effect both the spacing, the instantaneous areas involved, and the dielectric constant of the rubber) and the use of a suitable voltage, the charge per unit of area on the outer surface of the roll 36 may be so proportioned as to secure the maximum ink transfer effect at the printing point without any chance of arcing, as there is no follow-up current to support arcing evenif arcing conditions are otherwise present at the printing zone.

In these ilrst two embodiments of my inventions the variable high potential source might the typecylinder I l and be capable of supplying a voltage of anywhere trede. the type cylinder 5,0, are such as to facilifrom 4,000 volts up at the desired current output of 100 to 200 milliamperes, as for example being variable through a range of from 5,000 to 20,000 volts. Control of `current transfer conditions at the printing point is effected by control of the flow of space current from each'increment of area of the printing surface to prevent arcing, something which could not be done rby the resistances 22 and 42 alone. This matter is more fully described and claimed in my copending application No. 564,574, (which matured into Patent No. 2,520,504 August 29, 1950), delivery of a predetermined quantity of electricity to each increment of surface of the rolls or cylindrical members engaging the web being controlled in the first case by the leak through resistance of the current path to the surface, and in the second case by the deposition on each increment of area of the surface of a predetermined quantity of charge which is carried on and retained by each such increment until it reaches the printing point.

'Ihe embodiment of my invention illustrated in Figure 4 employs'a field creating and arc preventing method and apparatus of a kind more fully disclosed and claimed in my application Serial No. 580,381 (now abandoned). The embodiment illustrated in Figure 4, however, again makes use of the light contact or kiss contact principle, with certain other modifications which constitute improvements. In order to keep this specification as b'rief as possible parts in Figure 4 analogous to parts fully described in Figure l will be given reference numerals :i higher than those used in Figures l and 2, and reference may be had to the earlier description to supplement the statements as to the construction and function of parts in Figure 4.

Referring now more particularly to this latter ilgure, the design bearing member is shown as a type cylinder 50 which is grounded throughout and inked by means comprising the trough or fountain 52 and inking rolls 55m-d. The web of paper 54 passes over a guide roll 05, over a grounded preconditioning member 55, which may be of sliver, in light contact with the ink film on the surface of the roll 50, in contact with the lower bearing or guide portion 06a. of a field defining and electrode protecting member 60, and then over a guide roll 53. The desired potential diiferential is developed by a variable high potential source 6i having its negative terminal grounded and its positive terminal connected through a shielded cabie 6l to a knife electrode 68. This electrode may be or any metal, preferably noncorrosive metal as stainless steel. The main body portion of the knife electrode is covered by the material of the member 06, which should be of very high specific resistivity and relatively low dielectric constant, as glass with a dielectric constant in the neighborhood of four, only the tip 68a of the electrode projecting into the air. 'Ihe downwardly depending portions 66a and 66D serve not only as eld confining members, but also as positive means to prevent a workman from accidentally touching the hot electrode 68a. In this form of my invention the edge 68a of the electrode 68 is spaced more than two inches, preferably six or eight inches, from the type cylinder 50; and a potential differential is used between the electrodes which may be in the neighborhood of 150,000 volts. Prevention of arcing results from the wide spacing between the electrodes, and conditions around the negative electate electric printing.

While rubbing of a web fof paper across a well polished plate glass surface results in little changel in the electrical condition of the web, I have found that maximum control'of preconditioning v of the web can be achieved by having the web so arranged that it does not contact any surface -between its contact with the preconditioning means 55 and the point where it reaches the Accordingly, as is readily apparent from the drawing, the downwardly depending portion 66b is shorter ythan the portion 66a, so that the web does not contact the lower face or surface of the -portion 66h at all duringv its movement, preferably being spaced 1A; to 1A of an inch from such lower surface. That is, the depending portion 66h has field confining and protective functions only, whereas the portion 66a has the additional function of guide means for the web.

In order to readily adjust the contact of the web with the ink film on the cylinder 50 at the printing point I provide means for effecting fine adjustments of the vertical position of the guide member 66a, the direction of movement of the web being such that, during printing, the guide.

means comprising the portion 66a always serve to deflect or deform thel path of travel of the web somewhat below its straight line of travel between the element 55 and the guide roll 58. In order to effect this adjustment I mount the member 66 on a yoke or bracket 69 which is threaded on to a threaded shaft 10. This shaft is mounted for rotation in the end of a rigid bracket 'H forming part of the frame of the press or being otherwise rigidly supported. The shaft 70 yis provided with a handwheel lila at its upper end, and rotation of this handwheel, through interaction between the threaded shaft and bracket 69, effects upward or downward movement of the member 66 and thus of the guide portion 66a thereof. Arrangement of the guide portion on the opposite side of the printing space from the element 55, and use of a vertically adjustable mounting of this type, provides micrometer adjustment of the contact of the web 54 with the ink film on the raised portions of the type cylinder 50. This provides a very convenient and effective means of having the light or kiss contact desired. It will be understood, of course, that in practical operation systems of the kind illustrated in the first and second embodiments of my inventions heretofore described would also incorporate some means for adjusting the spacing between the cylindrical members between which the web passes.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement maybe made without departing from the spirit and scope of the invention as disclosed in the appended claims.

Iclaim:

l. A printing couple comprising a rotating type cylinder provided on its circumference with design portons, means for inking said design portions, means electrically grounding said cylinder, guide means cooperatively arranged with respect to said cylinder, means for moving a web of print receiving material in contact with said guide means and in non-pressure contact with the ink on said design portions of said cylinder and at a lineal speed correlated to the relative speed of said cylinder, means operatively associated with said guide means and connected to the positive pole of a high potential electrical source and creating an electrical ileld of force the lines of force of which extend beyond said guide means to said cylinder and act to transfer ink from said design portions to said web of print receiving material, said guide means comprising a member formed of insulating material and having spaced leg portions one of which contacts said web after the latter has passed out of contact with the ink on said design portions of said cylinder while the other of which is out of contact with said web, the means that is operatively associated with said guide means comprising an electrode element having a free end located intermediate said legs of said guide means and an electrical connection between said element and the positive pole of a high potential electrical source.

10 2. A printing couple as defined in claim 1 and wherein means is provided for adjusting said member in a radial direction with respect to said cylinder.

WILLIAM J. HOOPER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,788,600 Smyser Jan. 13, 1931 1,820,194 Huebner Aug. 25; 1931 2,191,827 Benner Feb. 27, 1940 2,221,776 Carlson Nov. 19, 1940 2,224,391 Huebner Dec. 10, 1940 2,408,144 Huebner Sept. 24, 1946 

